The present disclosure generally relates to storage media disturbance compensation. More particularly, the present invention relates to storage media disturbance compensation using more than one sample rate.
When accessing and/or writing data to optical discs, magnetic tape, or other types of data storage media, disturbances can occur at certain frequencies, resulting in distorted read/write operations. To minimize the distortions, compensation filters are employed to attenuate or suppress the disturbances. High bandwidth filters may be implemented to address a wide range of fixed and dynamic disturbances. Alternatively, narrower bandwidth filters may be employed if all of the disturbances can be identified beforehand using modeling or predictive algorithms.
In the case of magnetic tapes, they suffer from lateral tape motion (LTM) disturbance. LTM disturbance comprises dynamic events relating to tape speed and reel rotation rates that change over the length of the tape. The tape drive used to perform read/write operations includes a read/write head. The read/write head is configured to follow a specific track of the tape for a given time period. For example, the read/write head may follow a servo track of the tape. However, the presence of LTM disturbance causes the read/write head to laterally shift up or down relative to the track being followed (in a direction perpendicular to the longitudinal length of the track). If the disturbances are strong enough, the read/write head may lose the track being followed. As a result, if the tape drive was writing data previously, it needs to stop writing data temporarily to prevent writing to the adjacent track. Or if the tape drive was reading data previously, it may fail to read the data back since the reader is partially reading data from the adjacent track, and the tape drive needs to rewind the tape and attempt the read-retries. Such result would be detrimental to correct and rapid read/write operations. As tapes move to higher track density, higher data transfer rates, or higher tape speeds, LTM disturbance becomes even more of a problem.